From 9dca45568331eb80111360619a491a3192cdc63d Mon Sep 17 00:00:00 2001 From: Peter Delevoryas Date: Mon, 20 Sep 2021 08:50:59 +0200 Subject: [PATCH] hw/arm/aspeed: Initialize AST2600 UART clock selection registers MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit UART5 is typically used as the default debug UART on the AST2600, but UART1 is also designed to be a debug UART. All the AST2600 UART's have semi-configurable clock rates through registers in the System Control Unit (SCU), but only UART5 works out of the box with zero-initialized values. The rest of the UART's expect a few of the registers to be initialized to non-zero values, or else the clock rate calculation will yield zero or undefined (due to a divide-by-zero). For reference, the U-Boot clock rate driver here shows the calculation: https://github.com/facebook/openbmc-uboot/blob/15f7e0dc01d8/drivers/clk/aspeed/clk_ast2600.c#L357 To summarize, UART5 allows selection from 4 rates: 24 MHz, 192 MHz, 24 / 13 MHz, and 192 / 13 MHz. The other UART's allow selecting either the "low" rate (UARTCLK) or the "high" rate (HUARTCLK). UARTCLK and HUARTCLK are configurable themselves: UARTCLK = UXCLK * R / (N * 2) HUARTCLK = HUXCLK * HR / (HN * 2) UXCLK and HUXCLK are also configurable, and depend on the APLL and/or HPLL clock rates, which also derive from complicated calculations. Long story short, there's lots of multiplication and division from configurable registers, and most of these registers are zero-initialized in QEMU, which at best is unexpected and at worst causes this clock rate driver to hang from divide-by-zero's. This can also be difficult to diagnose, because it may cause U-Boot to hang before serial console initialization completes, requiring intervention from gdb. This change just initializes all of these registers with default values from the datasheet. To test this, I used Facebook's AST2600 OpenBMC image for "fuji", with the following diff applied (because fuji uses UART1 for console output, not UART5). @@ -323,8 +323,8 @@ static void aspeed_soc_ast2600_realize(DeviceState *dev, Error **errp) } /* UART - attach an 8250 to the IO space as our UART5 */ - serial_mm_init(get_system_memory(), sc->memmap[ASPEED_DEV_UART5], 2, - aspeed_soc_get_irq(s, ASPEED_DEV_UART5), + serial_mm_init(get_system_memory(), sc->memmap[ASPEED_DEV_UART1], 2, + aspeed_soc_get_irq(s, ASPEED_DEV_UART1), 38400, serial_hd(0), DEVICE_LITTLE_ENDIAN); /* I2C */ Without these clock rate registers being initialized, U-Boot hangs in the clock rate driver from a divide-by-zero, because the UART1 clock rate register reads return zero, and there's no console output. After initializing them with default values, fuji boots successfully. Signed-off-by: Peter Delevoryas Reviewed-by: Joel Stanley [ clg: Removed _PARAM suffix ] Message-Id: <20210906134023.3711031-2-pdel@fb.com> Signed-off-by: Cédric Le Goater --- hw/misc/aspeed_scu.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/hw/misc/aspeed_scu.c b/hw/misc/aspeed_scu.c index 05edebedeb..d06e179a6e 100644 --- a/hw/misc/aspeed_scu.c +++ b/hw/misc/aspeed_scu.c @@ -119,6 +119,8 @@ #define AST2600_CLK_SEL3 TO_REG(0x308) #define AST2600_CLK_SEL4 TO_REG(0x310) #define AST2600_CLK_SEL5 TO_REG(0x314) +#define AST2600_UARTCLK TO_REG(0x338) +#define AST2600_HUARTCLK TO_REG(0x33C) #define AST2600_HW_STRAP1 TO_REG(0x500) #define AST2600_HW_STRAP1_CLR TO_REG(0x504) #define AST2600_HW_STRAP1_PROT TO_REG(0x508) @@ -681,6 +683,8 @@ static const uint32_t ast2600_a3_resets[ASPEED_AST2600_SCU_NR_REGS] = { [AST2600_CLK_SEL3] = 0x00000000, [AST2600_CLK_SEL4] = 0xF3F40000, [AST2600_CLK_SEL5] = 0x30000000, + [AST2600_UARTCLK] = 0x00014506, + [AST2600_HUARTCLK] = 0x000145C0, [AST2600_CHIP_ID0] = 0x1234ABCD, [AST2600_CHIP_ID1] = 0x88884444, }; -- 2.11.0